Camshaft phasers for varying the phase relationship between the crankshaft and a camshaft of an internal combustion engine are well known. In a typical vane-type cam phaser, a controllably variable locking pin is slidingly disposed in a bore in a rotor vane to permit rotational locking of the rotor to the stator under certain conditions of operation of the phaser and engine. A known locking pin mechanism includes a return spring to urge an end of the pin into a hardened seat disposed in the pulley or sprocket (pulley/sprocket) of the phaser, thus locking the rotor with respect to the stator. The rotor may be formed of aluminum, and a steel bushing is pressed and staked into the bore at a predetermined axial location to guide the pin. In a prior art embodiment, the pin is shouldered, which shoulder engages the rotor bushing as a limit stop to pin travel. In operation, the pin is forced from the bushing and well in the pulley/sprocket to unlock the rotor from the stator by pressurized oil supplied from a control valve, overcoming the seating spring, in response to a programmed engine control module (ECM). The oil may be applied to the end of the pin and/or to the underside of the shoulder via passages formed in the rotor and/or the pulley/sprocket.
A prior art phaser has several shortcomings that are overcome by an improved phaser in accordance with the invention.
First, the pin and the seat typically include mating annular bevels to center the pin in the seat and thereby minimize angular lash between the rotor and the sprocket while locked. If the pin is permitted to engage the seat fully, however, the pin may become jammed into the seat and not respond reliably to opening oil pressure, so the shoulder is provided on the prior art pin to limit travel thereof. It is known that, with repeated use, the pin shoulder can displace the rotor bushing axially, resulting in failure of the phaser. Therefore, means are needed to eliminate the need for a pin shoulder.
Second, to permit rotation of the rotor, the pin is retracted by pressurized oil flowing from the adjacent advance chamber via a channel in the sprocket face. However, in some instances the pressure build-up in the advance chamber is rapid enough and large enough that the pin becomes bound in the well before there is sufficient pressure to cause it to withdraw, thus causing the phaser to be unable to alter the valve phase as demanded. Therefore, means are needed to ensure that the pin will not be stuck in the locked position when rotor rotation is required.
Third, the prior art mechanism includes the locking pin and return spring in a blind bore in the rotor facing against the pulley/sprocket. This mechanism can be difficult to assemble reliably. Therefore, a simpler, easier means is needed for providing a locking mechanism in a vane-type cam phaser.
It is a principal object of the present invention to improve the reliability of unlocking of a cam phaser locking mechanism.